Museum/Gallery websites:

The Louvre, Paris
Metropolitan Museum of Art, NY
MOMA, NY
The Tate, London
The National Gallery of Art, London
The Art Institute of Chicago
The Saatchi Gallery, London
The Museum of Contemporary Art, Chicago


Art Magazines:

Art in America: http://www.artinamericamagazine.com/
Art Forum: http://artforum.com/
Art News: http://artnews.com/home/

MISC:

Great new general source for artists! http://www.theartstory.org/
excellent for information on all art periods and includes videos! http://smarthistory.khanacademy.org/
super art history resource: http://arthistoryresources.net/ARTHLinks.html
good reference for initial artist search: http://www.artchive.com/ftp_site_reg.htm
art dictionary: http://www.artlex.com/

humanities web (perfect for establishing historical context): http://www.humanitiesweb.org/human.php

Video Interviews
Art21: an excellent TV series featuring contemporary artists
http://www.pbs.org/art21/

Tate Shots: another excellent collection of short interviews of contemporary artists produced by the Tate Modern Gallery, London
http://www.tate.org.uk/context-comment/audio-video/search?page=2&f[0]=im_vid_31%3A2327